Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a proton exchange membrane (“PEM”) to provide ion transport between the anode and cathode.
In proton exchange membrane type fuel cells, hydrogen is supplied to the anode as fuel and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O2) or air (a mixture of O2 and N2). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which a solid polymer membrane has an anode catalyst on one face, and a cathode catalyst on the opposite face. The anode and cathode layers of a typical PEM fuel cell are formed of porous conductive materials, such as woven graphite, graphitized sheets, or carbon paper to enable the fuel to disperse over the surface of the catalyst of the fuel supply electrode. Typically, each electrode has finely divided catalyst particles, supported on carbon particles, to promote oxidation of hydrogen at the anode and reduction of oxygen at the cathode. Protons flow from the anode through the ion conductive polymer membrane to the cathode where they combine with oxygen to form water which is discharged from the cell.
The MEA is sandwiched between a pair of porous gas diffusion layers (“GDL”) which in turn are sandwiched between a pair of non-porous, electrically conductive elements or plates. The GDL may also be referred to as the base layer. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing the fuel cell's gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell must be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in a grouping of many cells into a stack. Higher power output may be achieved through using arrays of many individual fuel cell stacks or increasing the cell count in a single stack in order to provide high levels of electrical power.
Fuel cells have been pursued as a source of power for transportation because of their high energy efficiency and their zero greenhouse emissions to the environment. However, broad commercialization of the fuel cells has been met with many limitations, particularly in relation to the relatively high cost of the fuel cell catalyst. Some of catalyst metals as used in fuel cell applications include noble and transition metals, such as platinum, which are very expensive. An amount of about 0.3 to 4 milligrams per square centimeter precious metals such as platinum is often required for a conventional fuel cell catalyst. It has been estimated that the total cost of the precious metal catalysts is up to 75 percent (%) of the total cost of manufacturing a low-temperature fuel cell.